This invention relates generally to rolling element bearings and more particularly to the mounting of such bearings in gas turbine engines.
A gas turbine engine includes one or more shafts which are mounted for rotation in several bearings, usually of the rolling-element type. The bearings are enclosed in enclosures called “sumps” which are pressurized and provided with an oil flow for lubrication and cooling. The bearings in a gas turbine engine are usually a combination of roller and ball bearings. The roller bearings react radial loads of the shafts and the ball bearings react radial and thrust loads.
In operation, the shafts are subject to vibration and dynamic loads caused by rotor and shaft unbalance and by self-excited whirl (i.e. dynamic instability). It is known in the turbomachinery field to use squeeze film bearing dampers to reduce the adverse vibrations due to high-speed rotor dynamics. Typically, the outer race of a rolling-element bearing is fitted with a small radial clearance. The clearance is filled with oil, and hydrodynamic forces are generated by the motion of the bearing under the influence of unbalance or other excitation. The squeeze film acts as a nonlinear spring and damper system which can significantly reduce the dynamic loads and suppress dynamic instability. Typically, a squeeze film damper would be provided with piston rings to limit the leakage of oil from the clearance.
It is further known to provide the outer race of a rolling-element bearing with drain holes through which lubricating oil can escape. Such “drained outer race bearings” are known to reduce bearing heat generation. Combining a drained outer race with a typical dual piston ring squeeze film damper would be problematic because the circumferential oil film would interfere with the bearing oil drain holes.
Accordingly, there remains a need for a bearing incorporating the functions of both a drained outer race and a squeeze film damper.